Added geometry formula shower / calculator Goodie

**What does your instant answer do?**
This goodie shows geometric formulas (e.g. circle area) or calculates them if sizes are specified.

**What is the data source for your instant answer? (Provide a link if possible)**
The german "Tafelwerk", because it is a good formulary

**What are some example queries that trigger this instant answer?**
formula circle area
for more: see test file

**Is this instant answer connected to a DuckDuckHack [instant answer idea](https://duck.co/ideas)?**
Yes, https://duck.co/ideas/idea/1053/geometry-calculator.

**Which existing instant answers will this one supercede/overlap with?**
Not known yet

**Are you having any problems? Do you need our help with anything?**
Not yet

```
[x] Added metadata and attribution information
[x] Wrote test file and added to t/ directory
[] Verified that instant answer adheres to design guidelines(https://github.com/duckduckgo/duckduckgo-documentation/blob/master/duckduckhack/styleguides/design_styleguide.md)
[] Tested cross-browser compatability
[x] Tested only on Linux 64-bit Firefox
```
@pixunil currently the test files are purely for ensuring correct triggering and with goodies you can ensure the result HTML. You shouldn't need any CSS/JS in here (the tests won't run them anways) -- but we are currently working on frontend testing so we'll be updating all the tests whenever that is finished.

For now you should be okay to remove this stuff.

fwiw if you need access to a /share/ file, Goodies and Spice have access to their own share dir's using the `share()` function: `my $content = share('my_file.txt')->slurp();`